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The effect of ultrasound (US) pretreatment (0, 200, 400, 600, and 800 W) on the physicochemical, emulsification, and gelatinization characteristics of citric acid (CA)-treated whey protein isolate (WPI) was investigated. Size exclusion chromatography demonstrated that when compared with untreated WPI, US pretreatment promoted production of more molecular polymers in the CA-treated WPI. There was a reduction in particle size of CA-treated WPI with the increase of US power (0–800 W), whereas its free sulfhydryl content, surface hydrophobicity, and intrinsic fluorescence strength increased. Furthermore, compared with untreated WPI, emulsifying ability index and emulsifying stability index of CA-treated WPI were increased by 14.04% and 10.10%, respectively, at 800 W. Accordingly, US pretreatment promoted the gel formation of CA-treated WPI, and its gel hardness was increased by 28.0% with US power ranging from 0 to 800 W. Therefore, US and CA treatment can be considered as an effective way to improve the emulsifying and gelatinization characteristics of WPI.

Impact of extrusion pretreatment (50, 70, 90, 110 and 130 °C) on physicochemical, emulsifying properties and water holding capacity (WHC) of transglutaminase (TGase) cross-linked whey protein isolate (WPI) were investigated in this study. The results of molecular size distribution and SDS-PAGE proved that there were more macromolecular polymers formed in TGase cross-linked WPI after extrusion pretreatment (E-WPI-TGase) and the consumption of free amino groups for E-WPI-TGase was the largest at the extrusion temperature of 50 °C and 70 °C. As the extrusion temperature increased from 90 °C to 130 °C, particle size of WPI after extrusion pretreatment (E-WPI) was not changed significantly, compared with that of E-WPI-TGase (p > 0.05). In addition, the emulsifying properties, surface hydrophobicity and WHC of E-WPI-TGase were higher than those of WPI cross-linked by TGase (WPI-TGase) (p

Conjugated linoleic acid contains unsaturated fatty acids with multiple bioactivities, but it has poor oxidative and physical stabilities. Its emulsion was fabricated with glycosylated whey protein isolate and hydrolysates of glycosylated whey protein isolate to enhance its stability. An obvious decrease in peroxide value, thiobarbituric acid-reactive substances, particle size and creaming index of emulsion loaded by hydrolysates of glycosylated protein isolate with the increase of hydrolysis time. However, the absolute value of zeta-potential and interfacial adsorption rate of emulsion stabilized by hydrolysates of glycosylated whey protein isolate, were increased by 10.99 and 16.94% at hydrolysis time of 120 min, compared with emulsion loaded by glycosylated whey protein isolate. Thus, limited hydrolysis of glycosylated whey protein isolate as an effective method, remarkably improved the oxidative and physical stability of emulsion.